U.S. patent number 4,622,440 [Application Number 06/599,137] was granted by the patent office on 1986-11-11 for differential hearing aid with programmable frequency response.
This patent grant is currently assigned to In Tech Systems Corp.. Invention is credited to Martin J. Slavin.
United States Patent |
4,622,440 |
Slavin |
November 11, 1986 |
Differential hearing aid with programmable frequency response
Abstract
A differential input hearing aid with a programmable frequency
response provides the hard of hearing with the capability to listen
to individual conversations in the midst of high ambient background
noise, and to have the frequency response of the hearing aid
tailored to the individual user by programming the desired response
characteristics into the hearing aid by digital signals. The audio
inputs of two microphones are applied to a subtractive circuit with
the balance of the inputs being controllable. Digitally controlled
band pass filters with selectable band and selectable level of
amplification are provided.
Inventors: |
Slavin; Martin J. (Dix Hills,
NY) |
Assignee: |
In Tech Systems Corp.
(Hauppauge, NY)
|
Family
ID: |
24398380 |
Appl.
No.: |
06/599,137 |
Filed: |
April 11, 1984 |
Current U.S.
Class: |
381/313; 381/312;
381/330 |
Current CPC
Class: |
H04R
25/407 (20130101); H04R 2460/03 (20130101); H04R
25/603 (20190501); H04R 2225/61 (20130101); H04R
25/502 (20130101) |
Current International
Class: |
H04R
25/00 (20060101); H04R 3/00 (20060101); H04R
025/00 (); H04R 003/04 (); H03G 003/20 () |
Field of
Search: |
;179/17FD,17K,17E,182K
;181/129,130 ;381/58,60,68,92,110 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0064042 |
|
Nov 1982 |
|
EP |
|
0071845 |
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Feb 1983 |
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EP |
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3205685 |
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Aug 1983 |
|
DE |
|
57-42296 |
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Mar 1982 |
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JP |
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57-44396 |
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Mar 1982 |
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JP |
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57-57100 |
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Apr 1982 |
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JP |
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723221 |
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Feb 1955 |
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GB |
|
2057228 |
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Mar 1981 |
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GB |
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Other References
"Voice Operated Control Switch", elektor, Dec. 1979, vol. 5, pp.
12-40-12-41. .
"Active Filking-A Step Toward the Programmable Hearing Aid",
Hearing Instruments, vol. 33, No. 10, Oct. 1982, p. 20. .
"Method and Apparatus for Adapting the Transfer Function in a
Hearing Aid" PCT application WO83/02212, pub. Jun. 1983, Bisgaard
et al. .
Hosticka and Brodersen, MOS Sampled Data Recursive Filters Using
Switched Capacitor Integrators, vol. SC-12, No. 6, pp. 600-608
(Dec. 1977). .
Material Semiconductor Handbook, MF10 Monolithic Dual Switched
Capacitor Filter, pp. 9-121-9-222..
|
Primary Examiner: Rubinson; Gene Z.
Assistant Examiner: Byrd; Danita R.
Attorney, Agent or Firm: Blum Kaplan Friedman Silberman
& Beran
Claims
What is claimed is:
1. A hearing aid comprising a first microphone having an input
oriented in a first direction; a second microphone having an input
oriented in a second direction different from said first direction;
subtractive circuit means for receiving the audio outputs of said
first and second microphones and subtracting one of said audio
signals from the other to produce a net audio signal, balance
control means for electrically adjusting the input ratio of the
audio signals from said first microphone and said second
microphone, and an electro-acoustic transducer positioned to apply
an acoustic signal to the user of the hearing aid in response to
said net audio signal.
2. The hearing aid of claim 1, said first and second directions are
more than 90 degrees apart.
3. The hearing aid of claim 2, wherein said subtractive circuit
means is a differential input operational amplifier.
4. The hearing aid of claim 1, including a telephone input means
for permitting coupling of said hearing aid to a telephone.
5. The hearing aid of claim 1, including auxiliary input means for
permitting coupling of said hearing aid to an auxiliary audio
signal source.
6. The hearing aid of claim 1, including a voice-operated switch
(VOX) means coupled intermediate at least one of said microphones
and said electro-acoustic transducer for selectively actuating said
hearing aid in response to audio inputs, whereby power consumption
by the hearing aid is minimized.
7. The hearing aid of claim 1, wherein said balance control means
is adapted to cut off at least part of that portion of the net
audio signal represented by said second microphone, whereby sound
from distant sources is passed by said subtractive circuit
means.
8. A hearing aid comprising a first microphone having an input
oriented in a first direction; a second microphone having an input
oriented in a second direction different from said first direction;
subtractive circuit means for receiving the audio outputs of said
first and second microphones and subtracting one of said audio
signals from the other to produce a net audio signal, and
electro-acoustic transducer means positioned to apply an acoustic
signal to the user of the hearing aid in response to said net audio
signal, band pass filter means coupled intermediate said
subtractive circuit means and said electro-acoustic transducer
means for dividing said net audio signal into a plurality of
frequency bands, means for amplifying each said band by a selected
amount representative of the correction appropriate for the user of
the hearing aid, means for selectively setting the center frequency
and band width of at least one of said frequency bands, and means
for joining the outputs of said amplifying means to a corrected
audio signal.
9. The hearing aid of claim 8, and including digital means for
selectively setting said center frequency and band width including
an EPROM for storing the instructions for such setting.
10. The hearing aid of claim 9, including means for applying a
programmable signal to said EPROM for the selective programming
thereof.
11. The hearing aid of claim 9, wherein said EPROM is a plug-in
unit for the substitution of an EPROM programmed for a particular
user.
12. The hearing aid of claim 8, including digital means for setting
the amplification level of each of said amplifying means including
an EPROM for storing the instructions for such setting.
13. The hearing aid of claim 9, including digital means for setting
the amplification level of each of said amplifying means, said
EPROM storing instructions for control of such setting.
14. The hearing aid of claim 13, including means for applying a
programmable signal to said EPROM for the selective programming
thereof.
15. The hearing aid of claim 13, wherein said EPROM is a plug-in
unit for the substitution of an EPROM programmed for a particular
user.
16. The hearing aid of claim 8, wherein the band pass filter means
comprises switched capacitor filter circuits.
17. A hearing aid comprising microphone means for receiving an
audio signal; band pass filter means for dividing said audio signal
into a plurality of frequency bands, means for amplifying each said
band by a selected amount representative of the correction
appropriate for the user of the hearing aid; means for selectively
setting the center frequency of at least one of said frequency
bands to one of a plurality of desired values representative of the
correction appropriate for the user of the hearing aid, means for
joining the outputs of said amplifying means to a corrected audio
signal; and an electro-acoustic transducer positioned to apply an
acoustic signal to the user of the hearing aid in response to said
net audio signal.
18. The hearing aid of claim 17, including means for selectively
setting the bandwidth of said at least one of said bands to one of
a plurality of desired values representative of the correction
appropriate for the user of the hearing aid.
19. The hearing aid of claim 18, including means for selectively
setting the center frequency and bandwidth of a plurality of said
frequency bands.
20. The hearing aid of claim 18, and including digital means for
selectively setting said center frequency and band width including
an EPROM for storing the instructions for such setting.
21. The hearing aid of claim 20, including means for applying a
programmable signal to said EPROM for the selective programming
thereof.
22. The hearing aid of claim 21, wherein said EPROM is a plug-in
unit for the substitution of an EPROM programmed for a particular
user.
23. The hearing aid of claim 17, including digital means for
setting the amplification level of each of said amplifying means
including an EPROM for storing the instructions for such
setting.
24. The hearing aid of claim 23, including digital means for
setting the amplification level of each of said amplifying means,
said EPROM storing instructions for control of such setting.
25. The hearing aid of claim 24, including means for applying a
programmable signal to said EPROM for the selective programming
thereof.
26. The hearing aid of claim 23, wherein said EPROM is a plug-in
unit for the substitution of an EPROM programmed for a particular
user.
27. The hearing aid of claim 17, wherein the band pass filter means
comprises switched capacitor filter circuits.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a hearing aid and especially to
a hearing aid employing differential audio inputs combined with a
programmable filtered frequency response. While the art of hearing
aids is generally well known and well understood, hearing aid users
continue to suffer from the non-discriminating nature of hearing
aids, resulting in the equal amplification of both audio
information and background noise. Additionally, it is well known in
the medical arts relating to human audio function, that most
hearing loss does not take place equally across the audio frequency
spectrum, but rather is localized at certain frequencies and to
certain levels.
While hearing aids have taken various forms in an attempt to both
cancel background noise and to more accurately customize the
frequency response of the hearing aid to its particular user, these
attempts have resulted in hearing aids that require constant
adjustment by their owners as well as extended and elaborate set-up
procedures.
Accordingly, it is desirable to provide a hearing aid having
differential audio inputs coupled with a programmable frequency
response to provide the hard of hearing with the capability to
listen to individual conversations in the midst of high ambient
background noise, and to have the frequency response of the hearing
aid tailored to the individual user in an expedited and low cost
manner.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the present invention, an
improved hearing aid having differential audio inputs and a
programmable frequency response is provided. The hearing aid
includes two small microphones which are used to pick-up the sound;
the first microphone is placed at the front of the unit and the
second microphone is placed at the rear of the unit. The output of
these two microphones are coupled to a differential amplifier. The
differential amplifier amplifies only the difference signal, which
is a subtraction of the signal of the first microphone from the
signal of the second microphone, and is adjustable by a balance
control to permit selected deactivation of the subtraction feature.
A telephone pick-up input and an auxiliary signal input is provided
to enable the user to have access to a wide variety of signal
sources. The output of the differential amplifier is coupled to a
voice activated switch (VOX), which is sensitive to signal level
changes, and which is used to control power to the later amplifier
portions of the unit, thereby helping to conserve the hearing aid
battery source.
The output of the VOX is coupled to an array of switched capacitor
filter circuits. These circuits provide the required controlled
frequency response based on pre-programmed digital information
which is stored within the hearing aid in an electrically
programmable read only memory (EPROM). The information may be
stored in the EPROM through an input jack or the EPROM can be a
plug-in unit. The switched capacitor filter circuits permit the
breakdown of the applied audio signal by digital processing into a
series of frequency bands of selected width and center frequency as
determined by the digital information stored in the EPROM. The
selective amplification of the bands as required to deal with the
hearing deficiency of the wearer is also set by the information
stored in the EPROM. The output of the amplified bands are joined
into a corrected audio signal.
The joined, amplified outputs of the switched capacitor filter
circuits are then coupled into an amplifier circuit having a
built-in squelch means, so as to allow the user to set the
threshold of the signal that will be passed through the hearing
aid. The output of the squelching amplifier is then coupled through
a final signal amplifier having a means for adjusting the overall
volume, and the output of the final amplifier is further coupled to
drive an earphone.
Accordingly, it is an object of the invention to provide an
improved hearing aid.
Another object of the invention is to provide an improved hearing
aid having differential audio inputs to enable the selective
cancelling of background noise.
A further object of the invention is to provide an improved hearing
aid having a digital programmable frequency response which can be
set through the use of plug in EPROMS.
Still another object of the invention is to provide an improved
hearing aid which is readily adapted to the user.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent in the specification.
The invention accordingly comprises the features of construction,
combination of elements and arrangements of parts which will be
exemplified in the construction hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to
the following description taken in connection with the accompanying
drawings, in which:
FIG. 1 is a block diagramatic circuit diagram of the instant
invention;
FIG. 2 is a diagramatic sectional view taken along the longitudinal
center line through a hearing aid constructed in accordance with
the present invention; and
FIG. 3 is an in part block, in part circuit diagram of an
embodiment of a switched capacitor filter usable in the hearing aid
constructed in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, a block circuit diagram of the apparatus
of the present invention is shown, wherein, a front microphone 10
is connected through an input buffer 20 to the positive input 26a
of differential input amplifier 26. A rear microphone 12 is
connected through a buffer 22 to the negative input 26b of
differential input amplifier 26. The front microphone 10 and rear
microphone 12 are connected to differential amplifier 26 in a
subtractive manner, so that any sound which appears at both the
front microphone 10 and the rear microphone 12 with equal amplitude
will, ideally, be cancelled out. This arrangement provides the
hearing aid with a background noise cancelling function, since most
background noise will originate at a point of sufficient distance
from the listener such that it will arrive at both the front
microphone 10 and rear microphone 12 at substantially the same
time.
Differential balance control 28 is provided coupled to differential
amplifier 26 in order to adjust the ratio of the subtraction
circuit between the front microphone 10 and the rear microphone 12.
This permits balance for maximizing subtraction, although full
elimination of all noise is difficult if not impossible. In
addition, it permits creating an imbalance or even eliminating the
input of one microphone so that background noise is selectively
received by the user. Where the user wishes to pick up close
conversations, such as conversations at a table in a noisy
restaurant, maximum subtraction would be selected by adjusting
balance control 28. Where the user is walking in the street,
minimum subtraction might be selected since it would be desirable
to pick up distant noises such as vehicle horns or traffic noise.
In a restaurant, such background noise could override and block out
close conversation in the absence of the subtraction feature in
accordance with the invention.
The differential amplifier 26 is also provided with a telephone
pick-up input 14 which is buffered through input buffer 18 and an
auxiliary pick-up input 16 which is buffered through input buffer
24. The output of the differential amplifier 26 is then coupled to
a voice operated switch (VOX) 30. VOX 30 is set to detect minimum
input threshold levels, and is used to control power to the
electronic components of the hearing aid, thereby saving battery
power when the unit is not in use, and when there are no sounds to
be amplified. Thus, the power from battery 38 and switch 40, as
indicated by arrow 39a, is applied to power buffers 18, 20, 22 and
24, differential amplifier 26 and VOX 30 as shown by arrows 39a.
When VOX 30 is actuated by a minimum input threshold level from
differential amplifier 26, power is applied from VOX 30, as
indicated by arrow 39c, to circuit elements 32, 34, 36, 42 and 48
as indicated by arrows 39c.
The output of VOX 30 is an analog signal which is then coupled to a
switched capacitor filter circuit 32. The switched capacitor filter
circuit 32 permits digitally controlled processing of analog audio
signals. Circuit 32 may include a single integrated hybrid MOS
device, such as the National Semiconductor MF 10 universal
monolithic dual switched capacitor filter made of operational
amplifiers, capacitors and MOS switches. The device uses ratioed
capacitors formed in a common integrated circuit substrate, the MOS
switch applying the input signal to a first capacitor and then
connecting the first capacitor to a second capacitor while
disconnecting the input to the first. The result is controlled
charging of the second capacitor by a selected frequency band
present in the input. A group of band pass filters will be provided
covering the desired audio range with the band of each filter being
digitally adjustable. The output of each band pass filter is
applied to a digitally adjustable amplifier which serves to
separately amplify each selected band in accordance with the needs
of the user. The outputs of the respective amplified frequency
bands are combined at the output to circuit 32 to produce a
corrected audio signal.
The switched capacitor filter circuit 32 operates under the command
of a microprocessor control circuit 34 by numerically imposing the
desired frequency response transfer function (selection of the
bands and of degree of amplification of each band) on the input
signal received from the VOX 30. The microprocessor control circuit
34, receives its instructions from an electrically programmed read
only memory (EPROM) 36. In standard operation, an individual with a
hearing problem would have his hearing tested with a computerized
audiometer. The audiometer would measure hearing loss within the
parameters of center frequency or frequencies of hearing loss, band
width of frequency of hearing loss about each center frequency and
percentage of hearing loss at each center frequency. The
computerized audiometer would transform this information into
numeric values representative of center frequency, band width and
amplification for each band. These numeric values would then be
digitally programmed, by the computerized audiometer, into a form
suitable for storage in an EPROM and for setting switched capacitor
filter circuit 32. Two approaches are available for programming
EPROM 36 to the correction needs of the user. In the first, an
input jack 56 would be provided coupled to EPROM 36 through
microprocessor 34 for applying the programming signal to the EPROM
36 from an output of the computerized audiometer. In the second
approach, the EPROM 36 is adapted to be unplugged from the hearing
aid circuit and plugged into a computerized audiometer for
programming. The programmed EPROM would then be unplugged from the
computerized audiometer and inserted into the programmable hearing
aid.
By the foregoing arrangement, a defect in the hearing of the user
would be correctable with precision. The precise frequency bands
requiring correction would be identified by the audiometer and the
degree of correction in each such band width would likewise be
identified. The correction in terms of bandwidth and center
frequency of each band and amplification thereof is stored in EPROM
36 to provide a hearing aid programmed to the needs of the
user.
Referring to FIG. 3, an in part block, in part circuit diagram of a
switched capacitor filter circuit 32 incorporating the switched
capacitor filter of the National Semiconductor MF 10 is depicted.
The input from VOX 30 is applied through variable resistor R.sub.1
to chip pin input 62, to provide one input to an operational
amplifier 64. The other input to operational amplifier 64 is
through chip pin input 66 which is connected to ground. A second
variable resistor R.sub.2 is connected between chip pin input 62
and 68 across operational amplifier 64. The output of operational
amplifier 64 is applied to the input of integrator 70, the output
of which is connected to chip output pin 72. A third varible
resistor R.sub.3 is connected between chip pins 62 and 72. A
variable clock circuit 74 is connected to integrator 70. The output
to the National Semiconductor switched capicitor filter, at chip
pin 72, is applied to a controlled operational amplifier 76, the
output of which is applied to squelch circuit 42.
In order to control the center frequency and bandwidth of switched
capacitor filter circuit 32, the frequency of clock 74 and the
values of resistors R.sub.1, R.sub.2 and R.sub.3 are digitally set
by control circuit 34 along lines 78, 80, 82 and 84, as by MOS
gates. Similarly, the degree of amplification of the passed band is
controlled by control circuit 34 through line 86 coupled to
operational amplifier 76.
In the case of the National Semiconductor device, the center
frequency of the output, f.sub.o, is equal to the clock frequency
divided by 50 or 100, depending on the setting of the inputs to the
circuit chip. The bandpass gain at f.sub.o is equal to -R.sub.3
/R.sub.1. The quality factor of the output, Q, equals f.sub.o /BW,
which equals R.sub.3 /R.sub.2. The bandwidth BW equals -3 dB
bandwidth of the bandpass output.
By using switched capacitor filters a relatively low cost filter
arrangement, requiring a minimal number of external components is
provided which permits digital programming. Such filters are highly
accurate since filter cut-off and frequency stability is directly
dependent upon the external clock stability.
Referring again to FIG. 1, the output of the switched capacitor
filter circuit 32 is then coupled through a squelch circuit 42.
Squelch circuit 42 is adjusted through the use of a squelch control
44 to allow the user to set the threshold of the signal that will
be listened to by the user. The output of the squelch circuit 42 is
then coupled through the master volume control 46, through the
output amplifier 48 and to the earphone 59.
Referring now to FIG. 2, a longitudinal diagramatic section view of
the present invention can be seen, wherein the differential balance
control 28, squelch control 44, and master volume control 46 are
mounted within the hearing aid case 54 so that they are still
accessible when the hearing aid case 54 is closed. Master power
switch 40 is coupled to master volume control 46. The battery 38 is
mounted within the hearing aid case 54, as is the switched
capacitor filter circuit 32, microprocessor control circuit 34, and
EPROM 36. EPROM 36 may be a plug-in unit. An amplifier circuit
package 52 which contains a plurality of operational amplifiers
used in the present invention for amplifying and buffering the
audio signal, is also mounted within the hearing aid case 54. Front
microphone 10 and rear microphone 12 are positioned within the
hearing aid case 54 so that front microphone 10 has access to sound
through the front microphone sound port 10a, and rear microphone 12
has access to sound through the rear microphone sound port 12a.
Sound ports 10a and 12a may be oriented to face in different
directions preferably more than 90 degrees apart. Earphone 50 is
mounted within the hearing aid case 54 so that it will fit within
the human ear canal when the hearing aid case is placed behind the
ear. While the embodiment depicted has several external controls,
if desired, only a volume control can be provided, the other
controls being programmed by means of control circuit 34 and EPROM
36, or pre-set by a manual internal adjustment.
It is clear from the foregoing that a differential audio input
hearing aid with a programmable frequency response can be
constructed according to the invention, allowing an individual with
a hearing loss to be provided with a low cost and personally
calibrated hearing aid.
It will thus be seen that the objects set forth above, and those
made apparent from the preceeding description, are effectively
attained and, since certain changes may be made in the above
construction without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended
to cover all the generic and specific features of the invention
herein described and statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
* * * * *